1. Field of the Invention
The present invention relates to methods of manufacturing a color filter and patterned substrate for use in, e.g., a field emission display device, fluorescent display device, plasma display (PDP), and liquid crystal display device. The present invention particularly relates to a color filter manufacturing method using a plurality of small photomasks, a patterned substrate manufacturing method, and the small photomask.
2. Description of the Related Art
A color filter for use in a color liquid crystal display device or the like is an essential member of the color liquid crystal display device or the like, and has functions of improving the image quality of the liquid crystal display device and giving each pixel a corresponding primary color. A filter segment or black matrix forming this color filter is manufactured as follows. That is, after a glass substrate or the like is coated with a photosensitive material, the excess solvent is removed by drying. Subsequently, the photosensitive material is irradiated with an active energy line via a photomask for pixel formation by, e.g., proximity exposure using an ultra-high-pressure mercury lamp. Consequently, the portion irradiated with the energy is cured (negative type) or the alkali solubility is increased (positive type), thereby removing a portion to be dissolved by an alkali solution or the like. A color filter is manufactured by repeating this process for each color.
Recently, the color liquid crystal display devices have formed a large market of liquid crystal color television displays, car navigation displays, and notebook PCs integrated with liquid crystal displays. The color liquid crystal display devices are also widely used as desktop PC monitors and television monitors that offer energy- and space-saving features. With the spread of the color liquid crystal display devices in general markets, demands for improving the color reproduction characteristics are increasing.
Also, to increase the contrast, a black matrix is generally formed between filter segments of the individual colors of the color filter. Recently, to solve the environmental problems, decrease the reflection, and reduce the cost, a resin black matrix formed by dispersing a light-shielding dyestuff in a resin is attracting more attention than a chromium metal black matrix. However, the resin black matrix has the problem that the light-shielding performance (optical density) is lower than that of the chromium metal black matrix.
To improve the color reproduction characteristics of the color filter and the light-shielding performance of the black matrix, it is necessary to increase the content of a dyestuff in a photosensitive coloring composition or increase the film thickness. However, if the content of a dyestuff is increased in a conventional method such as proximity exposure by which ultraviolet light or the like from an ultra-high-pressure mercury lamp is used as an active energy source as a light source, the problems such as the decrease in sensitivity and the deterioration of the development properties and resolution arise. Also, if the film thickness is increased, the exposure light does not reach the bottom of the film, and this poses the problems that, e.g., the linearity and sectional shape of the filter segments and black matrix deteriorate. Note that in the description of the present invention, the filter segments refer to individual coloring pixels of red, green, and blue, and the black matrix refers to a light-shielding black thin-line pattern for dividing these filter segments. Note also that light (a laser beam) from a laser as an exposure light source will simply be referred to as a laser hereinafter.
On the other hand, with the spread of the color liquid crystal display devices, demands for reducing the cost of the color filter are increasing. In the above-mentioned proximity exposure method, an ultra-high-pressure mercury lamp is generally used as a light source, and illuminating light whose illumination unevenness is eliminated by a fly-eye lens or microlens is converted into parallel light by a collimator lens. A photomask and a substrate on which a photosensitive resin layer such as a color resist is formed are arranged with a spacing of a few ten μm to a few hundred μm. The parallel light is emitted from above the photomask, thereby transferring the pattern of the photomask onto the substrate.
As described above, the proximity exposure method using an ultra-high-pressure mercury lamp requires no projecting exposure system. Since the apparatus configuration is very simple, the apparatus cost is low. Also, the same substrate area as the photomask can be exposed by one shot. Therefore, the method has the advantage that the tact is short when using a large photomask having almost the same size as that of the substrate. However, as the screen size of a product using the color filter increases, or to attach a number of large screens to one large-sized transparent substrate, the size of the photomask must further be increased. Since upsizing the photomask increases the manufacturing cost, it is important to reduce the cost of the photomask.
As a method of reducing the manufacturing cost of the photomask, patent reference 1 has disclosed a maskless exposure method that uses a laser as a light source and forms a two-dimensional image by relative scanning while modulating the light based on image data. Patent reference 2 has disclosed a laser exposure apparatus to be used to form the black matrix of the color filter. Since the laser exposure method can form pixels without using any expensive photomask, a large cost down can be expected. However, the laser exposure method using no photomask makes it difficult to develop a spatial modulation element to be used in exposure and a photosensitive resin composition suitable for the laser. In addition, fine patterns having good shapes are difficult to form. Furthermore, in the method described in patent reference 1, the exposure sensitivity must be increased by forming an oxygen-blocking film.
Patent reference 3 has disclosed an inkjet method capable of simultaneously printing three colors, i.e., R, G, and B by using coloring resin compositions of these colors as inks. Since the three colors can be printed at the same time, wastage of the materials is little. In addition, a reduction in environmental load and a large cost down can be expected because the pixel formation process is shortened. However, the inkjet method has the problem that a coloring layer printed by an ink ejector has not a flat shape but a projecting shape.